Luminescent materials for detecting X-rays and gamma-rays are a critical component for many medical imaging systems. However, present scintillator- semiconductor X-ray detectors have a poor match of scintillator light (approximately 400 nm) and photodiode response (lambda/max approximately 1,000 nm) which limits their performance. Detectors will be developed using a new scintillator, tellurium doped cadmium sulfide, realized in large (approximately 500 cm3), high quality single crystal boules by modified Vapor Phase Growth (mVPG) technology. CdS:Te is a rugged (4 Mho), dense (4.8 g/cm3) material whose bright (approximately 70% of NaI:TI), moderately fast (less than 300 ns), red (730 nm) luminescence is well matched to Silicon PhotoDiode (SiPD) sensitivity. Five tasks are proposed: (1) Develop the MVPG technology to produce large, high quality single CdS:Te crystals; (2) Synthesize and sublimate CdS and CdTe component material; (3) Produce MVPG single CdS:Te crystals varying growth conditions and Te content; (4) Measure the CdS:Te luminescent, optical, and structural properties with growth condition; and (5) Construct and evaluate prototype CdS:TeSiPD X-ray detectors for medical applications. In Phase II the CdS:Te MVPG technology will be optimized to produce high- quality, rugged, compact, low-power photon detectors. PROPOSED COMMERCIAL APPLICATION: Potential commercial application not available.